Coherence and Groundstate Properties of Highly Correlated f-Electron System: Kondo Lattice and Heavy Fermion Studies (Materials Research)

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This research effort is focused on establishing a better understanding of the unusual phenomena, i.e., heavy fermion, Kondo and Kondo lattice, spin fluctuation and mixed valent behavior, which appear in highly correlated f-electron systems. Such phenomena are commonly associated with a delocalization of the f-electrons due to a f-electron hybridization with other f- electrons or spd-electrons. The high temperature behavior associated with these systems seems to be well described by single ion models; however, at low temperatures these systems display coherent fermi liquid-like behavior. This research is directed at studying the salient features associated with this coherent groundstate. Measurements of the temperature and hydrostatic pressure dependence of the electrical resistivity, specific heat, magneto-transport coefficients and magnetic susceptibility on a select number of mixed valent and heavy fermion systems are planned. These measurements will be supplemented by measurements of the temperature dependence of the thermal electric power and thermal expansion along with room temperature crystal structure studies. The objective of this research is to establish the role played by the indirect f-f and f-spd exchange interactions, and other factors such as crystal field levels, the Kondo temperature, etc., on both the coherent state and on the nature of long range correlations, e.g., superconductivity and magnetic order, within this groundstate.